Great Skuas Research Articles

Activity patterns of wintering Great Skuas Stercorarius skua

Capsule Great Skuas Stercorarius skua wintering in different areas spent different amounts of time in flight (foraging or searching for food) and so may be experiencing different feeding conditions.Aims To compare the daily percentage of time spent in flight (foraging or searching for food) between different wintering areas.Methods In 2008, loggers equipped with a saltwater sensor were deployed on adult Great Skuas at three colonies in the northeast Atlantic, and the data used to compare foraging activity between the five main wintering areas.Results The five areas used by 22 Great Skuas in winter were widely separated, from the northwest Atlantic to northwest Africa, and differ substantially in oceanography. The main difference in foraging effort among areas for individuals that were site-faithful was that the percentage of time per day spent in flight off northwest Africa was much lower than elsewhere. Among five birds that travelled between wintering areas, one reduced the percentage of time in flight after switching from Iberia to northwest Africa.Conclusion The data suggest that feeding conditions were better off northwest Africa than elsewhere, at least during winter 2008/09. This allowed Great Skuas wintering in that region to spend more time resting, so probably reducing their overall energy expenditure.

A trial of three harness attachment methods and their suitability for long-term use on Lesser Black-backed Gulls and Great Skuas

Tracking devices are useful in studying the movement and behaviour of birds throughout the year. However, the effects of device attachment must be monitored for bird welfare and the scientific veracity of information gathered. We report on a trial of three different harness types (leg-loop, body and wing) for attaching GPS devices to Lesser Black-backed Gulls Larus fuscus and of a leg-loop harness on Great Skuas Stercorarius skua. This trial evaluated the functionality of the device whilst deployed, harness retention and the effects of each harness on the birds. The leg-loop harness prevented the devices from charging, due to feathers overlapping their solar panels, and individuals of both species shed this attachment during the first breeding season. For Lesser Black-backed Gull, devices functioned properly when attached using body and wing harnesses; foraging behaviour and territory attendance of birds were similar to the findings of other studies. Despite small sample sizes, annual adult survival rates for Lesser Black-backed Gull were similar to published estimates, suggesting harnesses had no deleterious effects. The wing harness has a smaller amount of skin contact than the body harness, and a non-constricting fit that better accommodates changes in body size. The wing harness was therefore considered the most appropriate for long-term studies.

Feather corticosterone levels on wintering grounds have no carry-over effects on breeding among three populations of great skuas (Stercorarius skua).

Environmental conditions encountered by migratory seabirds in their wintering areas can shape their fitness. However, the underlying physiological mechanisms remain largely unknown as birds are relatively inaccessible during winter. To assess physiological condition during this period, we measured corticosterone concentrations in winter-grown primary feathers of female great skuas (Stercorarius skua) from three breeding colonies (Bjørnøya, Iceland, Shetland) with wintering areas identified from characteristic stable isotope signatures. We subsequently compared winter feather corticosterone levels between three wintering areas (Africa, Europe and America). Among females breeding in 2009, we found significant differences in feather corticosterone levels between wintering areas. Surprisingly, levels were significantly higher in Africa despite seemingly better local ecological factors (based on lower foraging effort). Moreover, contrary to our predictions, females sharing the same wintering grounds showed significant differences in feather corticosterone levels depending on their colony of origin suggesting that some skuas could be using suboptimal wintering areas. Among females wintering in Africa, Shetland females showed feather corticosterone levels on average 22% lower than Bjørnøya and Iceland females. Finally, the lack of significant relationships between winter feather corticosterone levels and any of the breeding phenology traits does not support the hypothesis of potential carry-over effects of winter feather corticosterone. Yet, the fitness consequences of elevated feather corticosterone levels remain to be determined.

The status of breeding seabirds on the Isle of Tiree, Argyll, 2004-13

Annual monitoring of breeding seabirds on the Isle of Tiree 2004-13 revealed significant declines in the numbers of Northern Fulmar Fulmarus glacialis, Common Guillemot Uria aalge, Razorbill Alca torda and Black-legged Kittiwake Rissa tridactyla at the main seabird colony of Ceann a' Mhara. Numbers of Herring Gull Larus argentatus and Lesser Black-backed Gull L. fuscus also declined significantly across the island over the same period, whilst numbers of Common Gull L. canus increased significantly. Most other breeding seabirds including European Shag Phalacrocorax aristotelis, Black Guillemot Cepphus grylle, Little Tern Sternula albifrons, Arctic Tern Sterna paradisaea and Black-headed Gull Croicocephalus ridibundus remained stable or showed non-significant declines. Breeding was confirmed for the first time on Tiree by single pairs of Great Skua Stercorarius skua and Atlantic Puffin Fratercula arctica. Annual estimates of breeding success were recorded for six species. There were complete breeding failures of Black-legged Kittiwake in 2007-08, Arctic Tern in 2004-05 and Little Tern in 2006, although all three species had higher breeding success in 2009-13.

British Ornithologists' Union Records Committee: 42nd Report (October 2013)

British Ornithologists' Union Records Committee: 42nd Report (October 2013)

Influence of wintering area on persistent organic pollutants in a breeding migratory seabird

As apex marine predators, seabirds are often sampled to monitor bioaccumulative persistent organic pollutants (POPs) in the marine environment. Despite the restrictions on use and production of many POPs, concern remains about levels of these chemicals present in marine biota due to their potential toxicity. Many seabird species are migratory, and although overwinter- ing area has been hypothesized to affect the accumulation of POPs, few have studied the contri- bution of exposure in the wintering area on the POP burdens of seabirds. This study investigated the impact of wintering area on concentrations and patterns of organochlorines (OCs) and poly- brominated diphenyl ethers (PBDEs) in plasma of breeding great skuas Stercorarius skua from 3 colonies; Bjornoya (Svalbard), southeast Iceland and Shetland (Scotland). To do so, stable iso- tope values of primary feathers grown during the winter were used in conjunction with geolocator data (n = 16) to assign untracked individuals (n = 122), to 3 wintering areas (America, Europe and Africa). Birds wintering in Africa had lower plasma concentrations of many OCs and PBDE 47 compared to the other areas. Nevertheless, the influence of wintering area differed between con- taminants and between breeding colonies. We conclude that although wintering area had a significant effect on both concentrations and patterns of POPs, its influence was small in compar- ison to differences in exposure to these pollutants at breeding colonies, but that accumulation of POPs during the winter may be important for specific populations of seabirds.

Polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) in seven different marine bird species from Iceland

Data on distribution, concentration and trends of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs) is scarce in biota from the sub-Arctic region of the Atlantic. The present study is an investigation on PBDE and HBCD concentrations in eggs from seven marine bird species from Iceland, i.e. common eider (Somateria mollissima), arctic tern (Sterna paradisaea), guillemot (Uria aalge), fulmar (Fulmarus glacialis), lesser black-backed gull (Larus fuscus), great black-backed gull (Larus marinus) and great skua (Stercorarius skua). Concentrations of sum PBDEs ranged from 44ngg−1fat in eider eggs to 2400ngg−1fat in great skua eggs. The contribution of different PBDE congeners to the sum concentration differed between species. Concentration of HBCDs (sum of α−,β− and γ−HBCD) ranged from 1.3ngg−1fat in arctic tern eggs to 41ngg−1fat in great black-backed gull. PCA on PBDE and HBCD shows different trends between the two BFR groups, further indicating different sources/usage. Investigations on any potential health or population effects of environmental pollutants on the great skua are advised since both the PBDE and HBCD concentrations are high.

Ecosystem-based management objectives for the North Sea: riding the forage fish rollercoaster

AbstractDickey-Collas, M., Engelhard, G. H., Rindorf, A., Raab, K., Smout, S., Aarts, G., van Deurs, M., Brunel, T., Hoff, A., Lauerburg R. A. M., Garthe, S., Haste Andersen, K., Scott, F., van Kooten, T., Beare, D., and Peck, M. A. Ecosystem-based management objectives for the North Sea: riding the forage fish rollercoaster. – ICES Journal of Marine Science, 71: . The North Sea provides a useful model for considering forage fish (FF) within ecosystem-based management as it has a complex assemblage of FF species. This paper is designed to encourage further debate and dialogue between stakeholders about management objectives. Changing the management of fisheries on FF will have economic consequences for all fleets in the North Sea. The predators that are vulnerable to the depletion of FF are Sandwich terns, great skua and common guillemots, and to a lesser extent, marine mammals. Comparative evaluations of management strategies are required to consider whether maintaining the reserves of prey biomass or a more integral approach of monitoring mortality rates across the trophic system is more robust under the ecosystem approach. In terms of trophic energy transfer, stability, and resilience of the ecosystem, FF should be considered as both a sized-based pool of biomass and as species components of the system by managers and modellers. Policy developers should not consider the knowledge base robust enough to embark on major projects of ecosystem engineering. Management plans appear able to maintain sustainable exploitation in the short term. Changes in the productivity of FF populations are inevitable so management should remain responsive and adaptive.

Dietary versus Maternal Sources of Organochlorines in Top Predator Seabird Chicks: An Experimental Approach

We examined the relative importance of dietary sources and maternal transfer on organochlorine concentrations (∑OCs) in Great skua chicks (Stercorarius skua) in Shetland by food supplementing parents with known wintering area. We predicted that experimental chicks (whose parents were supplemented) should have (i) higher growth rates and, (ii) lower ∑OCs due to growth dilution effect and/or due to being fed with less contaminated food compared to control chicks. We also predicted a significant influence of maternal wintering area on chicks' ∑OCs. Plasma ∑OCs of adults, assessed prior to the manipulation, significantly differed between wintering areas of birds. Chicks were weighed every 5 days and plasma ∑OCs were assessed at 20 days old. Based on nitrogen and carbon stable isotope analysis, the supplementary food contributed on average 20% of the dietary protein of the chicks. Although experimental chicks experienced better developmental conditions, supplementary food did not alleviate their organochlorine burden. Nevertheless, chicks whose mothers wintered in Europe showed ∑OCs 50% higher than chicks whose mothers wintered in Africa. Moreover, based on the positive relationship between ∑OCs of chicks and females, the contaminant load of Great skua chicks in Shetland appears to be more influenced by maternal transfer than by trophic transfer.

Organohalogen contaminants and Blood plasma clinical–chemical parameters in three colonies of North Atlantic Great skua (Stercorarius skua)

The present study compares blood plasma clinical–chemical parameters (BCCPs) in birds from three geographically distinct North Atlantic Great skua (Stercorarius skua) colonies. Birds from these sites bioaccumulate different POP (persistent organic pollutant) concentrations and that enabled us to compare Great skua BCCPs in different exposure scenarios. Persistent organic pollutants (organochlorines: PCB, DDT, chlordanes, HCB, HCH, mirex and brominated flame retardants: PBDEs) and nineteen BCCPs were analysed in 114 adult Great skuas sampled during summer 2009 in North Atlantic colonies at Bjørnøya (n=42), Iceland (n=57) and Shetland (n=15). Specimens from Bjørnøya had the highest blood plasma concentrations of all contaminant groups followed by Iceland and Shetland birds, respectively (ANOVA: p<0.05). Most of the 19 BCCP parameters followed the pattern of colony differences found for contaminants, with Bjørnøya having the highest concentrations. However seven BCCPs, the three liver enzymes ALKP, ALAT and GGT as well as bile acids, cholesterol, sodium and potassium, did not differ between colonies (ANOVA: p>0.05). Therefore correlation analyses of these seven BCCPs vs. POPs were done on the combined colony data while the analyses of the remaining 12 BCCPs were carried out for each colony separately. The analyses of combined colony data showed that the blood plasma concentration of liver enzymes ALAT and GGT increased with increasing concentrations of ΣPBDE and ΣHCH, HCB and ΣCHL, respectively (all Pearson's p<0.05). In Great skuas from Shetland, the important osmotic transport protein albumin increased with increasing concentrations of ΣPCB and ΣDDT, while total blood plasma protein increased with ΣPCB, ΣDDT, ΣHCH and HCB concentrations (all Pearson's p<0.05). In both Bjørnøya and Iceland skuas, blood plasma pancreatic enzyme amylase decreased with increasing ΣHCH concentrations while the erythrocyte waste product total bilirubin in blood plasma increased with increasing ΣHCH and ΣPBDE concentrations in Iceland Great skuas (all Pearson's p<0.05). In Bjørnøya birds, blood plasma urea from protein metabolism (reflects kidney function) increased with increasing ΣPBDE concentrations (Pearson's p<0.05). Furthermore, a redundancy analysis showed that 10.6% of the variations in BCCPs could be explained by the variations in POP concentrations. Based on these results we suggest that liver and renal functions could be negatively affected by different POP compounds. It is, however, uncertain if the colony BCCP differences and their relationship to POP concentrations reflect health effects that could have an overall impact on the populations via reduced survival and reproduction parameters.

Perfluoroalkyl substances in eggs and plasma of an avian top predator, great skua (Stercorarius skua), in the north Atlantic

Temporal, biological, and environmental factors affecting accumulation of perfluoroalkyl substances (PFASs) are poorly understood in comparison with legacy lipid-soluble persistent organic pollutants. Temporal and biological comparisons of PFAS concentrations were made in great skuas (Stercorarius skua), a marine apex predator. Concentrations of 16 PFASs were quantified, including C4-C10 perfluorosulfonates (PFSAs), perfluorooctanesulfonamide (PFOSA), and C5-C14 perfluorocarboxylates (PFCAs). Concentrations of PFASs (ng/g wet wt) were significantly higher in eggs collected in Shetland in 2008 compared with 1980 for most compounds. However, the magnitude of the differences was small, with a mean increase of 3 ng/g. Levels of PFASs in great skuas were low compared with those of other seabirds in similar ecological niches; and in contrast to other contaminants measured in the same eggs, concentrations of PFASs did not correlate with trophic level. Concentrations of PFASs in adult plasma were significantly higher in males than in females for most PFASs. This suggests that maternal transfer through egg laying may be a significant mode of elimination of PFASs in female great skuas. The low concentrations of PFASs in eggs and plasma compared with other halogenated organic contaminants and other species suggest that great skuas do not bioaccumulate PFASs to the same extent as some other seabirds.

Diurnal seabird movements at Cabo Carvoeiro (Peniche, Portugal): observations in early October 2012

The ecology and movements of seabirds are still inadequately understood, mainly because they can rarely be studied efficiently from land. The potential of Cabo Carvoeiro (Peniche, Portugal) for monitoring seabird movements from land is poorly known internationally, as few results from this site have been published in English. Here we present data from standardised counts in October 2012 and draw attention to recent organised seabird counts in Portugal. Despite unfavourable weather conditions for concentrating seabirds towards land, we observed a strong passage of Northern Gannet Morus bassanus, Cory's Shearwater Calonectris diomedea, Great Skua Stercorarius skua, and Balearic Shearwater Puffinus mauretanicus (mean morning passage of 252, 99, 19, and 21 birds / hour, respectively). Manx Shearwater Puffinus puffinus, Sooty Shearwater P. griseus and Great Shearwater P. gravis occurred regularly in low numbers. Extrapolation indicates that thousands of seabirds passed daily within a few kilometres from land. The high counts of some species and the fairly high species diversity observed by us and in the RAM (Rede de observação de Aves e Mamiferos marinhos) initiative show that Cabo Carvoeiro is an outstanding site for monitoring and studying seabirds in the eastern Atlantic, as it is also located further south in the flyway than most other seawatch points. We hope this note will inspire ornithologists from other countries to participate in standardised seabird counts at Cabo Carvoeiro and other Portuguese sites.

Predator‐avoidance behaviour in a nocturnal petrel exposed to a novel predator

Many species of bird recognize acoustic and visual cues given by their predators and have complex defence adaptations to reduce predation risk. Recognition of threats posed by specific predators and specialized anti‐predation behaviours are common. In this study we investigated predator recognition and anti‐predation behaviours in a pelagic seabird,Leach'sStorm‐petrelOceanodroma leucorhoa, at a site where predation risk fromGreatSkuasStercorarius skuais exceptionally high. Leach's Storm‐petrels breed in burrows and come on land only at night. Counter‐predator adaptations were investigated correlatively in relation to changing natural light levels at night, and experimentally in relation to nocturnal visual and acoustic signals fromGreatSkuas. Colony attendance byLeach's Storm‐petrels was attuned to changes in light conditions at night and was highest when nights were darkest. This behaviour is likely to reduce predation risk on land; however, specific recognition ofGreatSkuas and specialized defence behaviours were not found.Leach's Storm‐petrels, in particular apparently non‐breeding individuals, were entirely naïve to the threat posed byGreatSkuas and were captured easily in a variety of different ways, on the ground and in the air. Lack of specialized behavioural adaptations inLeach's Storm‐petrels againstGreatSkuas may be because spatial overlap of breeding distributions of these species appears to be a rare and recent phenomenon.

Individual variation in biomarkers of health: Influence of persistent organic pollutants in Great skuas (Stercorarius skua) breeding at different geographical locations

Persistent organic pollutants (POPs) have been shown to cause adverse effects on a number of biomarkers of health in birds. POPs may impair immune function and alter the stress response, defined as a suite of behavioral and physiological responses to environmental perturbations. Recent studies have also proposed that POPs can induce oxidative stress. Nevertheless, there is a lack of studies simultaneously assessing the potential damaging effects of POPs on the latter biomarkers. In this study, we examined the contribution of legacy (organochlorines; (OCs)) and emerging (flame retardants; PBDEs) POPs to individual variations in stress levels (feather corticosterone), humoral immunity (plasma immunoglobulin Y levels) and oxidative stress occurring in three breeding colonies of a top predator seabird, the Great skua (Stercorarius skua), distributed from temperate regions to the high Arctic: Shetland (60oN), Iceland (63°N) and Bjørnøya (74°N). Our results demonstrated that plasma concentrations of OCs in Great skuas from Bjørnøya are among the highest in North Atlantic seabirds, with up to 7900μg/kg (ww) ∑OCs. Yet, a latitudinal gradient in POP levels was observed with all compounds being significantly higher in Bjørnøya than in Iceland and Shetland (on average 4–7 fold higher for OCs and 2.5–4.5 for PBDEs, respectively). Contrary to our predictions, skuas breeding at the least contaminated site (i.e., Shetland) experienced the poorest physiological condition; i.e., the highest levels of stress hormones (25% higher) and oxidative stress (50% higher) and the lowest immunoglobulin levels (15% lower) compared to the two other colonies. Finally, our results failed to point out consistent within-colony relationships between biomarkers of health and POPs. Overall, it is suggested that other ecological factors such as food availability could constrain physiological indicators more than anthropogenic contaminants.

Aves, Stercorariidae, Chilean Skua Stercorarius chilensis Bonaparte, 1857: First documented record for the state of Espírito Santo, southeastern Brazil

This study presents the first documented record of the Chilean Skua Stercorarius chilensis for the state of Espírito Santo in southeast Brazil. A debilitated bird was found during regular beach monitoring in July 2011 on Ubu Beach, Anchieta municipality. It received veterinary treatment and was successfully rehabilitated and released at Guanabara Beach, in the same municipality.

Beak tax to control predatory birds in the Faroe Islands

A beak tax was levied in the Faroe Islands from 1742 until 1881. Every man between the ages of 15 and 50 was obliged each year to submit to the authorities one raven's beak or two beaks of a crow, great skua or greater black-backed gull. A fine was imposed if a man failed in this obligation. The tax was repealed in 1881, after which men were paid for the beaks, and records of the beaks exist until 1934. A total of about 800 beaks submitted annually did not appear to deplete the bird populations, however the increasing human population from around 1800 increased the pressure on the bird populations which then declined rapidly from around 1850. A brief increase in the number of beaks occurred after 1881 when men were paid for the beaks and after that time the populations declined again. The population of crows declined more dramatically than the raven population while the great skua had declined to four breeding pairs when it was protected in 1897. The number of beaks submitted is correlated to the island size, the habitat index and the number of sheep. The smack fishery from the 1880s resulted in a better economy and better survival of the ewes in the lambing season which led to less interest in shooting the four bird species that predated on lambs. The bird populations have recovered even though the Faroese are still allowed to hunt them all the year round.

Persistent organic pollutants and their effects on Arctic seabirds

Persistent organic pollutants (POPs) and their degradation and metabolic byproducts have been found in high levels in blood and tissues of several Arctic seabird- and mammal species (Glaucous gull (Larus hyperboreus), Ivory gull (Pagophila eburnea), Great skua (Stercorarius skua), Arctic fox (Alopex lagopus) and Polar bear (Ursus maritimus). The POPs include both old (PCBs, DDTs and CHLs) and new contaminants (polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs) and polychlorinated naphthalenes (PCNs). While the contaminants which are subjected to global bans or restrictions are decreasing, new and emerging chemicals are increasing in Arctic birds and mammals. Several species are also exposed to contaminant metabolites (p, p-DDE, OH- and MeSO2-PCBs and OH-PBDEs) that, at times, are more bioactive than their precursors. Of high concern are the potential effects of the POPs and their metabolites in exposed seabird species. The present presentation summarizes recent studies on biological effects in relation to POP exposure in seabirds.

Flight speeds of migrating seabirds in the Strait of Gibraltar and their relation to wind

Wind is an important selective agent in bird migration. In this study, we investigated the influence of wind on the air speed of pelagic seabirds in the Strait of Gibraltar by means of radar measurements. The birds were identified visually at the species level. A total of 354 radar tracks of migrating birds were analysed, with an average tracking time of 147 s per target. An interspecific comparison under neg- ligible wind speeds showed a slight increase of air speed in the order from Cory's Shearwater, a typically gliding species (12.8 m s -1 ), Balearic Shearwater (gliding with flapping, 14.7 m s -1 ), gannets (flap-gliding, 15.0 m s -1 ), Great Skua (flapping, 16.0 m s -1 ) to auks (fast flapping, 17.4 m s -1 ). All of the studied species decreased their air speed with increasing wind increment (ground speed minus air speed), and this occurred in following winds slightly less than in opposing winds. Auks adjusted air speed to wind increment only in opposing winds, suggesting that auks are not able to reduce their high air speed in following winds due to extre- mely high wing loading.

Wintering areas of Great Skuas Stercorarius skua breeding in Scotland, Iceland and Norway

Capsule Great Skuas Stercorarius skua breeding in Scotland, Iceland, and Norway, winter in different areas. Aims To assess the winter distribution of adult Great Skuas breeding in different countries. Methods Geolocation data-loggers were deployed on breeding adults at colonies in Shetland (Scotland), southeast Iceland, and Bjørnøya (Norway) in 2008. Loggers were recovered when birds returned to breed the next year and downloaded data were processed to indicate the location of each individual throughout the winter period. Results Adult Great Skuas from Scotland wintered off northwest Africa and southern Europe. Adults from Iceland mostly wintered off Canada, with small numbers visiting northwest Africa and Europe. Although adults from Bjørnøya (Norway) migrated to similar areas to birds from Iceland, a slightly greater proportion wintered off Europe, and most used areas further north than birds from Scotland. Although three birds studied over consecutive winters used the same small area in consecutive years, four moved between different areas within one winter. Conclusion Great Skuas show clear variation in migrations among breeding regions, and some evidence of individual consistency.

Ways of developing acoustic signals in birds

An analysis of Russian and foreign literature data on the ways of developing acoustic signals in birds is presented. The physical analysis of acoustic signals is given for six species of birds: long-tailed skua (Stercorarius longicaudus Uicill), herring gull (Larus argentatus Pontopp.), sabine’s gull (Xema sabini sab.), curlew sandpiper (Calidris ferruginea Pantopp.), red-throated diver (Gavia stellata Pontopp.), and black-throated diver (Gavia aterica L.). Signals of embryos, baby birds, and adult birds are considered. The denervation of the syrinx in baby and adult birds was investigated to obtain a pattern of generation of acoustic signals in the absence of syrinx innervation. The temporal-frequency signal characteristics are compared to those of decapitated birds. The examples of acoustic signals of these birds confirm the significant role of the physical characteristics of morphological structures participating in the generation of acoustic signals in birds.